The present invention relates to a multi-slice MR (Magnetic Resonance) imaging method and apparatus in which a forcible recovery pulse can be practically applied to the "multi-slice technique".
In Japanese Patent Application No. 2-45448 (1990) (Japanese Patent Application Laid Open No. 60-151548 (1985)), a method is disclosed which comprises the steps of repeating a pulse sequence in a repeat time TR while varying a phase encoding gradient so as to fill k-space, the pulse sequence applying a first 90.degree. pulse (selective excitation pulse) and n 180.degree. pulses (non-selective inversion pulses) to acquire n sets of MR data in parallel which are different in T.sub.2 relaxation; acquiring the MR data sets in parallel which respectively fill n k-spaces (multi-echo technique) to obtain simultaneously n images which are different in contrast; and, subsequent to the pulse sequence of the multi-echo technique, applying a 180.degree. pulse (non-selective inversion pulse), and then applying a second 90.degree. pulse (selective excitation pulse) if n is odd, or a second 90.degree. pulse and a subsequent 180.degree. pulse (non-selective inversion pulse) if n is even, thereby enabling the repeat time TR to be shortened.
The distinction between "selective" and "non-selective" as regards the above-described selective excitation pulse and non-selective inversion pulse is defined as follows: "Selective" refers to the case in which a gradient magnetic field is applied simultaneously with an RF (Radio Frequency) pulse to validate the RF pulse for only an object slice to be imaged; and "non-selective" refers to the case in which an RF pulse is applied without simultaneously applying a gradient magnetic field, thus validating the RF pulse for slices other than the object slice to be imaged.
In addition, the second 90.degree. pulse, and the second 90.degree. pulse and the subsequent 180.degree. pulse are referred to as "forcible recovery pulses" because these pulses are for forcibly turning the residual transverse magnetization after data acquisition back to longitudinal magnetization.
Japanese Patent Application No. 2-45448 (Laid Open No. 60-151548) mentioned above discloses a method in which the forcible recovery pulse for forcibly turning transverse magnetization back to longitudinal magnetization is applied to the "multi-echo technique" and furthermore, suggests application of the forcible recovery pulse to the "multi-slice technique".
However, since the method disclosed in Japanese Patent Application No. 2-45448 (Laid Open No. 60-151548) employs non-selective inversion pulses, it cannot be practically applied to the "multi-slice technique".